<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link href="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/4.5.3/css/bootstrap.min.css" rel="stylesheet" />
  </head>
  <body>
    <style>
      div[class^='col'] {
        background-color: royalblue;
      }
      /* @media screen and (min-width: 576px) {
        body {
        }
      }
      @media screen and (max-width: 576px) {
        body {
        }
      } */
    </style>
    <div class="container">
      <div class="row">
        <div class="col-lg-3 col-sm-6">1</div>
        <div class="col-lg-3 col-sm-6">2</div>
        <div class="col-lg-6 col-sm-12">3</div>
      </div>
    </div>
    <!-- min-width:576px max-width -->
  </body>
</html>
